The invention relates to an improvement to a glow plug of the type generally known from GB 2489520 A or DE 10 2007 044 967 A1.
Glow plugs comprising a glow pencil which is movable in a longitudinal direction in relation to its housing can be used to measure the combustion chamber pressure. In order to protect the sensors and the electronics against hot combustion gases and to prevent combustion gases from leaking through an annular gap between the glow pencil and the housing, the glow plugs known from GB 2489520 A and DE 10 2007 044 967 A1 comprise a bellows that is attached to the glow pencil with its forward combustion-chamber-side end and to the housing with its rearward end.
Deposits of residual fuel on the bellows may restrict the movability of the glow pencil in relation to the housing. In order to handle such coking problems, the bellows of the glow plug known from DE 10 2007 044 967 A1 is coated with catalytic materials which promote the combustion of residual fuel. GB 2489520 A also refers to the problem of coking and teaches that a sealing element should be mounted between the forward end of the bellows and the housing. Due to the sealing element, combustion gases enter the annular space between the bellows and the housing in small quantities only, with the result that the risk of coking is reduced accordingly.